Protective-gap device



Dec. 10, 1940. J. SLEPIAN PROTECTIVE-GAP DEvicE Filed June 13, 1939WITNESSES:

n/wm

ATTORNEY Patented Dec. 10, 1940 UNITED STATES PROTECTIVE-GAP DEVICEJoseph Slepian, Pittsburgh, Pa, assignmto West- Mannfactnring oinghouseElectrlc &

East Pittsburgh, Pa., a corporation or Pennsyl:

vania Application June 13, 1939, Serial No. 278,844

7 Claims.

My invention relates to excess-voltage protective devices of the formwhich is sometimes referred to as the expulsion-gas discharge-tube type,in which an arc is formed within an insulating tube in the presence ofarc-responsive gasevolving insulating material which operates to createa blast which extinguishes the arc at the termination of theexcess-voltage conditions which produced the arc. Such tubes have arating dependent upon their breakdown-voltage and their ability tointerrupt arcs of a certain range of current-values, the maximumcurrent-rating being generally determined by the ability of the tube towithstand the rupturing forces of the excessive internal gaseouspressures which are produced by a heavy discharge, and the minimumcurrent-rating being determined by the ability of the relatively feeblelow-current blast to extinguish the low-current arc after the subfldenceof the excess-voltage surge which originally initiated the discharge.

My invention has particular reference to discharge-tubes, of theabove-described character, which are utilized, for protection againstexcessvoltage surges, in a connection, or on a system, in which neitherthe surge-current which is discharged during the existence of the surge,nor the so-called power-follow current, which tends to continue to flowin the ionized space created by the surge-discharge, is sufilcient toresult in a reasonably prompt extinction of the arc.

It is an object of my invention to combine such a discharge-tube devicewith another discharge-tube device which is differently electricallyconnected, and which is closely physically associated with the firstdischarge-tube device, so that there is an intercommunication of theblasts of ionized gases between the two dischargetube devices. Thus, thearcing of the one will sufilciently ionize the other; to initiate an arctherein, the electrical connections of the second discharge-tube devicebeing such that it will then discharge with an arc of a highercurrent-intensity, so that it will produce a blast which is strongenough, not only to extinguish its own arc, but to communicate itself tothe arc in the first tube, and thus extinguish both arcs.

One place where such a double-gap protective means is needed is on asubstantially ungrounded electric power-system, by which I mean a systemwhich is either normally insulated from ground, or which is normallyconnected to ground through a high impedance, either the groundingimpedance or (in a three-phase system) the total zerophase-sequenceline-impedance, however composed. In such a system, the power-followcurrent which may flow in an arcing ground, may be very small, rangingfrom merely the charging-current resulting from the capacity between theline-conductor and ground, to various magnitudes of ground-currentdepending upon the zero-phase-sequence impedance of the line, whichimpedance may be very high.

My invention is illustrated, in two illustrative forms of embodiment, inthe accompanying draw- 5 ing, wherein the two figures arecross-sectional views of two diiferent forms of the protective-gapassembly, respectively, with diagrammatic representations of a simpleexample of an electrical system to which the gap-assembly may beconnected.

For simplicity of explanation and illustration, I show my invention, inboth Fig. l and Fig. 2 of the drawing, as being applied to theprotection of an ungrounded single-phase power-line i, although theinvention is also applicable to the protection of other electricaldevices. The illustrated single-phase line i is supplied with power froma transformer 2, and which is protected by means of my presentinvention. The particular form of tubular gap-device which is utilizedis not significant, so long as there are utilized twophysically-associated gap-devices having intercommunicatingdischarge-openings, so that the ionized blast of one device maycommunicate itself to the other. The particular type of gapdevice whichis illustrated in both figures of the drawing consists of a fibre tube 3which is closed, at one end, by a metal terminal-cap l, the tube 3 beingopen at the other end. The fibre of which the tube is composed, is aninsulating material which has the property of evolving large quantitiesof substantially non-ionized gases or particles, in the presence of anare. This insulating tube 3 houses a resistor 5 and an inner metallicelectrode 6, with the resistor 5 disposed between the=-terminal-cap 4and the electrode 6. The metal terminal-cap I and the resistor 5constitute connecting-means for causing the inner metallic electrode 6,constituting one of the terminal electrodes of the tube, to project orextend inwardly into the tube so as to provide a shorter insidesparkover-distance than the outside sparkoverdistance, so that abreakdown or arcover will always occur inside of the tube. Between theelectrode 6 and the open end of the insulating tube 5, the particularillustrated tube contains a multi-slotted so-called difiuser plug 1which is also made of fibre, and which is separated from the electrode6, and from the open end of the tube 3, by annular spacers 8 and 9,respectively.

In accordance with my invention, I utilize two tubes such as the tubewhich has just been described, or discharge-gap tubes of any otherspecific formation, so long as they are of a type in which a blast isproduced for extinguishing the arc of the discharge. In Fig. 1, the twotubes are disposed in substantial alignment with each other, with thetwo open ends of the respective tubes facing each other, so that anyblast which 0 is produced in one tube will blow directly into the twotubes to the outside atmosphere. The

two ends of the metal coupling ll constitute the respectiveground-terminals of the two tubes.

In Fig. 2, the two tubes are disposed in sideby-side relationship, withtheir open ends joined by a pipe-like metal hardware or. coupling l3,which provides two substantially aligned passages l4 and I5 for therespective gas-blasts of the two tubes, so that the blast of one tube iscommunicated readily to the other tube, the coupler l3 being alsoprovided with a lateral vent It for venting the tubes to the outsideatmosphere.

While the tubes of both forms of embodiment of my invention are vented,as at [2 and it, respectively, the vents I2 and I6 are laterallydisposed and are preferably of such reduced crosssection that materialproportions of the gas-pressure and of the kinetic velocity of thegaseous blast, from the tube which breaks down first, will be directedinto the other tube. While the fibre insulating material evolvesun-ionized gaseous, and possibly event tiny solid, particles,nevertheless the gaseous blast which is expelled from any tube which isdischarging is highly ionized, at least as long as the arc is playingwithin the tube. As a consequence of this, the communication of theblast, from one tube to the other, ionizes the second tube and causesthe latter to break down at voltages which are far' below the normalbreakdown-voltage of the tube.

Various electrical connecting means may be utilized for providingdifferent electrical connections for the two tubes, so, that one of thetubes may break down first, and communicate its discharge to the othertube, causing the latter to break down even though abnormalvoltage-conditions do not appear on the second tube at the time, theconnections being such that, when the second tube breaks down, theamount of current which flows in the resulting arc will be larger thanthe current which flowed in the first tube before the second tube brokedown, thus avoiding the necessity for either tube interrupting its arcat the low current-conditions which were obtained when only the firsttube was discharging. These electrical connections can assume variousforms, the form of connection which is illustrated in both Figs. 1 and 2being a simple line-toground connection between the two respectiveline-conductors of the line I and ground, the central hardware orcoupler Ii or I3 being grounded, as indicated at I1, and the twoterminal-caps 4 being connected, one to one of the line-conductors l8and the other to the other line-conductor l9.

In operation, if an excessive voltage should appear upon one of theline-conductors l8 or IE, either by reason of a direct lightning-stroke,or by induction, or from any other cause, the associated tubulardischarge device will break down, momentarily connecting thatline-conductor to ground through the resistance 5 and the arc ordischarge which forms within the tube between the inner electrode 6 andthe grounded electrode H or 43, as the case may be. It will be notedthat the inner electrode 6, at the inner end of the resistor 5, extendsfar enough into the tube 3, from the closed end 4, to insure that abreakdown will always occur internally of the tube rather thanexternally thereof.

In the case of an absolutely ungrounded line, as shown, the power-followcurrent which follows in the wake of the surge-current discharge will beextremely small, amounting to only the charging-current of the line, so,that there would be a strong tendency for a tiny are or discharge tohang on, in the tube, for possibly a few cycles, 5 or even permanently,after such a surge-current discharge, except for the double-tubearrangement in accordance with my invention, whereby the discharge ofone of the tubes, under the circumstances mentioned, will immedil0 atelycommunicate itself to the other tube, ionizing the discharge-space ofthe second tube so that the second tube breaks down, even though anexcessive voltage is not impressed across its terminals 4 and II or it,as the case may be. 1 As soon as the second tube breaks down, there willbe two arcs in series, forming a low-resistance conducting path, throughthe two tubes, between the two line-conductors l8 and I9, thus producinga line-to-line short-circuit on the line I, and 20 drawing a heavypower-follow current which is of suflicient magnitude to enable thetubes to practically instantaneously extinguish their arcs.

While I have illustrated my invention in only two forms of construction,and with only a single 25 form of electrical connection, I wish it to beunderstood that such illustration is only illustrative,

so far as the general broader principles of my invention are concerned,and that many changes and substitutions may be made by those skilled 30in the art, without departing from the broader aspects of my invention.I desire, therefore, that the appended claims shall be accorded thebroadest construction consistent with their language and the prior art.

I claim as my invention:

1. Excess-voltage protective apparatus for an electrical device to beprotected, comprising a plurality of physically closely relatedexpulsion discharge-tubes; means for electrically different 40 lyconnecting said tubes to different conductors of" said protectedelectrical device, one of said tubes being susceptible of breaking down,at times, before another of said tubes; each tube comprising a tubularinsulating housing-structure and a pair 45 of normally electricallyinsulated terminal electrodes therefor, connecting-means for causing atleast one of said electrodes to project into the tube for a distancesufficient to insure that a breakdown shall always occur internally ofthe 50 tube rather than externally thereof, the internal discharge-spaceor spaces between the two electrodes within the bore of each tubularhousingstructure including arc-responsive gas-evolving insulatingmaterial; a physical communication- 55 means for causing ionizedparticles from one of said tubes, which may be discharging, to becommunicated to another of said tubes, which may not be discharging,whereby thelatter tube may be caused to discharge; and venting-meansphysically associated with said plurality of tubes.

2. Excess-voltage protective apparatus for an electrical device to beprotected, comprising tubemeans comprising a plurality of physicallyclosely related expulsion discharge-tubes; means for 55 electricallyconnecting said tube-means to said protected electrical device, saidtube-means and said connecting means providing a plurality of difierentdischarge-paths within said tube-means, at least one discharge-pathbeing responsive to 70 line-to-ground voltage while anotherdischargepath is responsive to line-to-line voltage; each tubecomprising a tubular insulating housingstructure and a pair of normallyelectrically insulated terminal electrodes therefor, connecting- 75means for causing at least one of said electrodes to project into thetube for a distance sufiicient to insure that a breakdown shall alwaysoccur internally of the tube rather than externally thereof, theinternal discharge-space or spaces between the two electrodes within thebore of each tubular housing-structure including arcresponsivegas-evolving insulating material; a physical communication-means forcausing ionized particles from one of said tubes, which may bedischarging, to be communicated to another of said tubes, which may notbe discharging, whereby the latter tube may be caused to discharge; andventing-means physically associated with said plurality of tubes.

3. The combination, with a substantially ungrounded multi-conductorelectrical line, of excess-voltage protective apparatus comprising aplurality of physically closely related expulsion discharge-tubes; meansfor connecting one of said tubes between one conductor of said line andground; means for connecting another of said tubes between anotherconductor of said line and ground; each tube comprising a tubularinsulating housing-structure and a pair of normally electricallyinsulated terminal electrodes therefor, connecting-means for causing atleast one of said electrodes to project into the tube for a distancesufficient to insure that a breakdown shall always occur internally ofthe tube rather than externally thereof, the internal discharge-space orspaces between the two electrodes within the bore of each tubularhousingstructure including arc-responsive gas-evolving insulatingmaterial; a physical communicationmeans for causing ionized blasts to beintercommunicated between said tubes and ventingmeans physicallyassociated with said plurality of tubes.

4. Excess-voltage protective apparatus for an electrical device to beprotected, comprising a plurality of physically closely relatedexpulsion discharge-tubes; means for electrically differently connectingsaid tubes to said protected electrical device, a first one of saidtubes being subj ect to a relatively weak initial power-follow currentif it breaks down first, while a second one of said tubes is subject toa power-follow current heavier than said initial power-follow current ifsaid second tube breaks down last, the discharge of the second tubecausing the discharge of the. first tube to clear itself; each tubecomprising a tubular insulating housingstructure and a pair of normallyelectrically insulated terminal electrodes therefor, connectingmeans forcausing at least one of said electrodes to project into the tube for adistance sufficient to insure that a breakdown shall always occurinternally of the tube rather than externally thereof, the internaldischarge-space or spaces between the two electrodes within the bore ofeach tubular housing-structure including arc-responsive gas-evolvinginsulating material; a physical communication-means for causing ionizedblasts to be intercommunicated between said tubes; and venting-meansphysically associated with said plurality of tubes.

5. Excess-voltage protective apparatus for an electrical device to beprotected, comprising two substantially aligned expulsion-blastdischargetubes. each tube having an open end, and the two open endsbeing disposed facing each, other; and means for electricallydifferently connecting said tubes to said protected electrical device,one of said tubes being susceptible of breaking down, at times, beforeanother of said tubes; each tube comprising a tubular insulatinghousing-structure and a pair of normally electrically insulated terminalelectrodes therefor, connecting-means for causing at least one of saidelectrodes to project into the tube for a distance suflicient to insurethat a breakdown shall always occur internally of the tube rather thanexternally thereof, the internal discharge-space or spaces between thetwo electrodes within the bore of each tubular housing-structureincluding arcresponsive gas-evolving insulating material.

6. Excess-voltage protective apparatus for an electrical device to beprotected, comprising a plurality of physically closely relatedexpulsion discharge-tubes; means for electrically differently connectingsaid tubes to different conductors of said protected electrical device,one of said tubes being susceptible of breaking down, at times, beforeanother of said tubes; each tube comprising a tubular insulatinghousing-structure and a pair of normally electrically insulated terminalelectrodes therefor, connecting-means for causing at least one of saidelectrodes to project into the tube for a distance sufficient to insurethat a breakdown shall always occur internally of the tube rather thanexternally thereof, the internal discharge-space or spaces between thetwo electrodes within the bore of each tubular housing-structureincluding arc-responsive gas-evolving insulating material; and a commonintermediate venting-outlet for venting both tubes so that ionizedblasts are intercommunicated between the two tubes.

'7. The combination; with a protected electrical device having firstvoltage-output terminals capable of delivering a relatively largepower-current when short-circuited and second voltage output terminalscapable of delivering a relatively smaller power-current whenshort-circuited; of excess-voltage protective apparatus comprising aplurality of physically closely related expulsion discharge-tubes; eachof said tubes comprising a pair of electrodes having spacedarcing-terminals, there being a separate arcing-space between its ownindividualpair of spaced arcing-terminals for each of the tubes, tubularinsulating means surrounding the respective arcing-spaces, andconnecting-means for causing at least one of the arcing-terminalsbounding each arcing-space to project into the tubular insulating meansa distance sufiicient to insure that a breakdown shall always occurinternally of the tubular insulating means rather than externallythereof, each arcing-space including arc-responsive gas-evolvinginsulating material; connecting-means for connecting two of said tubesin series-circuit relation across the first voltage-output terminals ofthe protected device; and connecting-means for connecting one of saidtwo tubes but not the other of said two tubes in a circuit across thesecond voltageoutput terminals of the protected device; the discharge ofsaid one of said two tubes causing a discharge of the other one of saidtwo tubes.

JOSEPH SLEPIAN.

